Eveline J. Bartowsky

Bacterial spoilage of wine and approaches to minimize it

Bacteria are part of the natural microbial ecosystem of wine and play an important role in winemaking by reducing wine acidity and contributing to aroma and flavour. Conversely, they can cause numerous unwelcome wine spoilage problems, which reduce wine quality and value. Lactic acid bacteria, especially Oenococcus oeni, contribute positively to wine sensory characters, but other species, such as Lactobacillus sp. and Pediococcus sp can produce undesirable volatile compounds. Consequences of bacterial wine spoilage include mousy taint, bitterness, geranium notes, volatile acidity, oily and slimy‐texture, and overt buttery characters. Management of wine spoilage bacteria can be as simple as manipulating wine acidity or adding sulfur dioxide. However, to control the more recalcitrant bacteria, several other technologies can be explored including pulsed electric fields, ultrahigh pressure, ultrasound or UV irradiation, and natural products, including bacteriocins and lysozyme.

Lactic Acid Bacteria as a Potential Source of Enzymes for Use in Vinification

Two key groups of organisms are involved in the production of red, white, and sparkling wine. The yeasts, typically strains of Saccharomyces cerevisiae , carry out the primary or alcoholic fermentation, in which sugars are converted to ethanol and CO2. Lactic acid bacteria (LAB), especially

Spoilage of bottled red wine by acetic acid bacteria

Aims: To determine the bacterial species associated with an outbreak of spoilage in commercially bottled red wine where the bottles had been stored in an upright vertical compared with horizontal position.

Comparative analysis of the Oenococcus oeni pan genome reveals genetic diversity in industrially-relevant pathways

BackgroundOenococcus oeni, a member of the lactic acid bacteria, is one of a limited number of microorganisms that not only survive, but actively proliferate in wine. It is also unusual as, unlike the majority of bacteria present in wine, it is beneficial to wine quality rather than causing spoilage. These benefits are realised primarily through catalysing malolactic fermentation, but also through imparting other positive sensory properties. However, many of these industrially-important secondary attributes have been shown to be strain-dependent and their genetic basis it yet to be determined.ResultsIn order to investigate the scale and scope of genetic variation in O. oeni, we have performed whole-genome sequencing on eleven strains of this bacterium, bringing the total number of strains for which genome sequences are available to fourteen. While any single strain of O. oeni was shown to contain around 1800 protein-coding genes, in-depth comparative annotation based on genomic synteny and protein orthology identified over 2800 orthologous open reading frames that comprise the pan genome of this species, and less than 1200 genes that make up the conserved genomic core present in all of the strains. The expansion of the pan genome relative to the coding potential of individual strains was shown to be due to the varied presence and location of multiple distinct bacteriophage sequences and also in various metabolic functions with potential impacts on the industrial performance of this species, including cell wall exopolysaccharide biosynthesis, sugar transport and utilisation and amino acid biosynthesis.ConclusionsBy providing a large cohort of sequenced strains, this study provides a broad insight into the genetic variation present within O. oeni. This data is vital to understanding and harnessing the phenotypic variation present in this economically-important species.

Screening of Lactobacillus spp. and Pediococcus spp. for glycosidase activities that are important in oenology.

Aims:  To assess glycosidase activities from a range of Lactobacillus and Pediococcus species and characterize these activities under conditions pertinent to the wine industry.

Genomic variations of Oenococcus oeni strains and the potential to impact on malolactic fermentation and aroma compounds in wine

Malolactic fermentation (MLF) is the bacterially driven decarboxylation of l-malic acid to l-lactic acid and carbon dioxide, and brings about deacidification, flavour modification and microbial stability of wine. The main objective of MLF is to decrease wine sourness by a small increase in wine pH via the metabolism of l-malic acid. Oenococcus oeni is the main lactic acid bacterium to conduct MLF in virtually all red wine and an increasing number of white and sparkling wine bases. Over the last decade, it is becoming increasingly recognized that O. oeni exhibits a diverse array of secondary metabolic activities during MLF which can modify the sensory properties of wine. These secondary activities include the metabolism of organic acids, carbohydrates, polysaccharides and amino acids, and numerous enzymes such as glycosidases, esterases and proteases, which generate volatile compounds well above their odour detection threshold. Phenotypic variation between O. oeni strains is central for producing different wine styles. Recent studies using array-based comparative genome hybridization and genome sequencing of three O. oeni strains have revealed the large genomic diversity within this species. This review will explore the links between O. oeni metabolism, genomic diversity and wine sensory attributes.

Microsatellite PCR profiling of Saccharomyces cerevisiae strains during wine fermentation

Aims:  Use of microsatellite PCR to monitor populations of Saccharomyces cerevisiae strains during fermentation of grape juice.

Genotypic diversity in Oenococcus oeni by high-density microarray comparative genome hybridization and whole genome sequencing.

Many bacteria display substantial intra-specific genomic diversity that produces significant phenotypic variation between strains of the same species. Understanding the genetic basis of these strain-specific phenotypes is especially important for industrial microorganisms where these characters match individual strains to specific industrial processes. Oenococcus oeni, a bacterium used during winemaking, is one such industrial species where large numbers of strains show significant differences in commercially important industrial phenotypes. To ascertain the basis of these phenotypic differences, the genomic content of ten wine strains of O. oeni were mapped by array-based comparative genome hybridization (aCGH). These strains comprised a genomically diverse group in which large sections of the reference genome were often absent from individual strains. To place the aCGH results in context, whole genome sequence was obtained for one of these strains and compared with two previously sequenced, unrelated strains. While the three strains shared a core group of conserved ORFs, up to 10% of the coding potential of any one strain was specific to that isolate. The genome of O. oeni is therefore likely to be much larger than that present in any single strain and it is these strain-specific regions that are likely to be responsible for differences in industrial phenotypes.

Microbial Formation and Modification of Flavor and Off-Flavor Compounds in Wine

The production of alcoholic beverages has a long history among humankind, with winemaking, as an example, dating back over 7,000 years. Even though the concept of transforming grape juice into wine does not appear difficult, it can be a complex process to ensure a delicious and stable product that does not spoil during storage. The true challenge for winemakers is to blend an ever-changing “menu” of grapes, soil, and climate with an evolving science of yeast and bacterial metabolism to produce the best possible expression of their chosen wine style. The vinification process used today is not vastly different from that used in the time of the ancient Egyptians and Greeks; however, modern-day winemakers have much more control at the various critical stages from the time and method of grape-picking to innovative maturation techniques. Many winemakers today use commercial yeast and bacteria starter cultures for alcoholic and malolactic fermentations. Selection of a “fit-for-purpose” starter strain has a pivotal role in optimizing flavor and aroma, and bottle and closure choice is another contributing factor to the characteristics of the finished wine. To produce the best wine with the desired style, flavor formation must be optimized and off-flavors development minimized. Wine aroma and flavor originate from the grape, yeast and bacterial metabolism of grape juice and wood (if used), and chemical reactions during maturation and storage. Several recent reviews cover numerous aspects of these areas (Swiegers et al. 2005; Swiegers and Pretorius 2005). Most of the yeast and bacterial metabolism discussed in this chapter is not necessarily specific to production of red or white wine and is applicable to all winemaking styles. An overview of the winemaking pathway for red and white grapes is given in Fig. 11.1.

Linking wine lactic acid bacteria diversity with wine aroma and flavour

In the last two decades knowledge on lactic acid bacteria (LAB) associated with wine has increased considerably. Investigations on genetic and biochemistry of species involved in malolactic fermentation, such as Oenococcus oeni and of Lactobacillus have enabled a better understand of their role in aroma modification and microbial stability of wine. In particular, the use of molecular techniques has provided evidence on the high diversity at species and strain level, thus improving the knowledge on wine LAB taxonomy and ecology. These tools demonstrated to also be useful to detect strains with potential desirable or undesirable traits for winemaking purposes. At the same time, advances on the enzymatic properties of wine LAB responsible for the development of wine aroma molecules have been undertaken. Interestingly, it has highlighted the high intraspecific variability of enzymatic activities such as glucosidase, esterase, proteases and those related to citrate metabolism within the wine LAB species. This genetic and biochemistry diversity that characterizes wine LAB populations can generate a wide spectrum of wine sensory outcomes. This review examines some of these interesting aspects as a way to elucidate the link between LAB diversity with wine aroma and flavour. In particular, the correlation between inter- and intra-species diversity and bacterial metabolic traits that affect the organoleptic properties of wines is highlighted with emphasis on the importance of enzymatic potential of bacteria for the selection of starter cultures to control MLF and to enhance wine aroma.